Push reamer

ABSTRACT

In some underground boring applications the exit location of the underground bore may be located such that drill pipe and material pipe sections cannot be conveniently deployed therefrom (e.g., a basement of a building, the inside of another pipe, or a small manhole space). In such applications, push reaming functionality is often the preferred method of reaming because the pipe section can be deployed and installed from a pit where the bore is started during a push reaming operation. The present disclosure provides a new push reaming drill head as well as a new method of push reaming.

This application is being filed on 15 Nov. 2013, as a PCT International patent application, and claims priority to U.S. Provisional Patent Application No. 61/726,999, filed Nov. 15, 2012, the disclosure of which is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to trenchless drilling equipment. More particularly, the present disclosure relates to tunneling equipment capable of reaming a pre-bored hole to enlarge the diameter of the hole.

BACKGROUND

Modern installation techniques provide for the underground installation of services required for community infrastructure. Sewage, water, electricity, gas and telecommunication services are increasingly being placed underground.

One method for installing underground services involves excavating an open trench. However, this process is time consuming and is not practical in areas supporting existing construction.

Other methods for installing underground services involve boring an underground hole. In some underground applications an underground hole is bored from above the ground surface and back up through the ground surface (e.g., horizontal drilling machines). In other applications the underground hole is bored from a first pit to an exit location, which may be a second pit (e.g., on grade drilling machines). Vermeer Manufacturing's PCT International Publication No. 2012/040190 (WO 2012/166905) and U.S. Pat. No. 7,942,217, U.S. Pat. No. 8,151,906 discloses a micro-tunneling system and apparatus capable of boring and back-reaming an underground micro-tunnel at precise grade and line, these publications are all hereby incorporated by reference in their entirety.

SUMMARY

In on grade application (drilling straight bores), a first pit is typically formed sufficiently large to allow for the set up drill apparatus which receives and deploys drill casings during boring, and the second pit is formed generally sufficiently large to deploy the pipe sections that are installed during a pullback reaming operation. However, in some circumstances the exit location of the underground bore may be located such that the pipe sections cannot be deployed therefrom (e.g., a basement of a building, the inside of another pipe, or a small manhole space under a busy roadway). In such applications, push reaming functionality is often the preferred method of reaming because the pipe section can be deployed and installed from the first pit during a push reaming operation.

One aspect of the present disclosure relates to a thrust/push reaming system for enlarging the diameter of a pre-bored hole. In one example, the reaming system includes a cutter mounting plate that is rotated by a rotational driver of the system about a central axis of rotation. The cutter mounting plate includes a front face having a peripheral portion that surrounds the axis of rotation. A plurality of reaming cutters is mounted to the peripheral portion of the front face. In one example, the reaming cutters can include bits (e.g., tri-cone bits) that are rotatable relative to the cutter mounting plate. In one example, the bits can each include a main body rotatably mounted on a shaft/pin secured to the cutter mounting plate, and a plurality of cutting elements (e.g., carbide buttons) embedded in or otherwise anchored to the main body. The system can also include a guide or centralizer that advances in front of the cutter mounting plate within the pre-bored hole during reaming. The guide is configured to fit within the pre-bored hole in advance of the cutter mounting plate so as to center the cutter mounting plate relative to the pre-bored hole. In one example, the centralizer can be a cylindrical sleeve having a hollow interior. An attachment structure (e.g., a plurality of robust bars, rods, plates, etc.) extends forwardly from the cutter mounting plate and connects the centralizer to the cutter mounting plate. In one example, the cutter mounting plate, the attachment structure and the centralizer can all rotate together as a unit about the central axis of rotation during reaming operations. In other examples, relative rotation can be provided between the centralizer and the cutter mounting plate such that during reaming the cutter mounting plate rotates to enlarge the hole while the centralizer does not rotate within the pre-bored hole. To allow for relative rotation, bearings can be provided between the centralizer and the attachment structure, between the attachment structure and the cutter mounting plate, or elsewhere. In one example, the centralizer is hollow to allow any cuttings or other material present in the pre-bored hole to pass through the centralizer to the cutter mounting plate. The cutter mounting plate can define one or more through-holes for allowing cuttings generated during reaming and/or material that passes through the centralizer to pass through the cutter mounting plate from the front side to a back side of the cutter mounting plate. A vacuum intake of a cuttings removal system can be provided near the back side of the cutter mounting plate for drawing-in material that passes through the through-holes and evacuates the material from the reamed hole. Gasketing can be provided between the vacuum intake and the back side of the cutter mounting plate to enhance suction. Fins or other structures can be provided on a front side of the cutter mounting plate for directing/lifting cuttings from the bottom of the reamed hole toward the through-holes. In one example, the reaming cutters define a cutting diameter that is at least 5, 10, or 20 percent larger than a cross-dimension (e.g., outer diameter) of the centralizer.

A variety of additional aspects will be set forth in the description that follows. The aspects can relate to individual features and to combinations of features. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad inventive concepts upon which the embodiments disclosed herein are based.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depiction of a push reaming apparatus having features in accordance with the principles of the present disclosure;

FIG. 2 is an enlarged view of a portion of FIG. 1;

FIG. 3 is a top elevation view of an alternative embodiment of a push reaming apparatus in accordance with the principles of the present disclosure;

FIG. 4 is a cross-sectional view along line 4-4 of FIG. 3;

FIG. 5 is a first end view of the push reaming apparatus of FIG. 3; and

FIG. 6 is a second end view of the push reaming apparatus of FIG. 3.

DETAILED DESCRIPTION

FIG. 1 shows a push reaming apparatus 20 having features in accordance with the principles of the present disclosure. The push reaming apparatus is configured to enlarge a pre-bored hole 200 using a push reaming process. During the push reaming process, the push reaming apparatus 20 reams the pre-bored bole 200 to create a reamed hole 202 having a larger diameter than the pre-bored bole 200.

Generally, the apparatus 20 includes a plurality of pipe sections 22 that are coupled together in an end-to-end relationship to form a drill string 24. Each of the pipe sections 22 includes a drive shaft 26 rotatably mounted in an outer casing assembly 28. A drill head 30 is mounted at a distal end of the drill string 24, while a drive unit 32 is located at a proximal end of the drill string 24. The drive unit 32 includes a torque driver adapted to apply torque to the drill string 24 and an axial driver for applying thrust or pull-back force to the drill string 24. Thrust or pull-back force from the drive unit 32 is transferred between the proximal end to the distal end of the drill string 24 by the outer casing assemblies 28 of the pipe sections 22. Torque is transferred from the proximal end of the drill string 24 to the distal end of the drill string 24 by the drive shafts 26 of the pipe sections 22 which rotate relative to the casing assemblies 28. The torque from the drive unit 32 is transferred through the apparatus 20 by the drive shafts 26 and ultimately is used to rotate a cutter mounting plate 33 of a push reaming unit 34 of the drill head 30. Optional skids 204 can be provided at bottom sides of the outer casing assemblies for assisting in centering the drill string within the reamed hole 202. Other types of centralizers could also be used.

The pipe sections 22 can also be referred to as drill rods, drill stems or drill members. The pipe sections are typically used to form an underground bore, and then are removed from the underground bore when product (e.g., piping) is installed in the bore.

The drill head 30 of the drilling apparatus 20 can include a drive stem 46 rotatably mounted within a main body 38 of the drill head 30. A distal end of the drive stem 46 is configured to transfer torque to the cutter mounting plate 33. A proximal end of the drive stem 46 couples to the drive shaft 26 of the distal-most pipe section 22 such that torque is transferred from the drive shafts 26 to the drive stem 46. In this way, the drive stem 46 functions as the last leg for transferring torque from the drive unit 32 to the push reaming unit 34. The outer casing assemblies 28 transfer thrust and/or pull back force to the main body 38 of the drill head. The drill head 30 preferably includes bearings (e.g., axial/thrust bearings and radial bearings) that allow the drive stem 46 to rotate relative to the main body 38 and also allow thrust or pull-back force to be transferred from the main body 38 through the drive stem 46 to the push reaming unit 34.

To assist in drilling, the tunneling apparatus 20 can also include a fluid pump 63 for forcing drilling fluid from the proximal end to the distal end of the drill string 24. In certain embodiments, the drilling fluid can be pumped through a central passage 45 defined through the drive shafts 26. The central passage 45 defined through the drive shafts 26 can be in fluid communication with at least one fluid delivery port provided at a front face of the cutter mounting plate 33 such that the drilling fluid is readily provided at a reaming interface of the push reaming unit 34.

During reaming, the cutter mounting plate 33 is rotated by the rotational driver of the drive unit 32 about a central axis of rotation 206. The cutter mounting plate 33 includes a front face 208 having a peripheral portion 210 that surrounds the axis of rotation 206. A plurality of reaming cutters 211 are mounted to the peripheral portion 210 of the front face 208. In one example, the reaming cutters 211 can include bits (e.g., tri-cone bits) that are rotatable relative to the cutter mounting plate 33. In one example, the bits can each include a main body rotatably mounted on a shaft/pin secured to the cutter mounting plate 33, and a plurality of hardened elements (e.g., carbide buttons) embedded in or otherwise anchored to the main body.

The system can also include a guide or centralizer 212 that advances in front of the cutter mounting plate 33 within the pre-bored hole 200 during reaming. The centralizer 212 is configured to fit within the pre-bored hole 200 in advance of the cutter mounting plate 33 so as to center the cutter mounting plate 33 relative to the pre-bored hole 200. In one example, the centralizer 212 has an outer diameter that is only slightly smaller than the diameter of the pre-bored bole 200. In one example, the centralizer 212 can be a cylindrical sleeve having a hollow interior 214.

An attachment structure 216 (e.g., a plurality of robust bars, rods, plates, etc.) extends forwardly from the cutter mounting plate 33 and connects the centralizer 212 to the cutter mounting plate 33. In one example, the cutter mounting plate 33, the attachment structure 216 and the centralizer 212 can all rotate together as a unit about the central axis of rotation 206 during reaming operations. In other examples, relative rotation can be provided between the centralizer 212 and the cutter mounting plate 33 such that during reaming the cutter mounting plate 33 rotates to enlarge the pre-bored hole while the centralizer 212 does not rotate within the pre-bored hole. To allow for relative rotation, bearings can be provided between the centralizer 212 and the attachment structure 216, between the attachment structure 216 and the cutter mounting plate 33, or elsewhere.

In one example, the centralizer 212 is hollow to allow cuttings or other material present in the pre-bored hole 200 to pass through the centralizer 212 to the cutter mounting plate 33 as the drill string is forwardly advanced (e.g., thrusted forwardly via thrust provided by the drive unit 32) during reaming. The cutter mounting plate 33 can define one or more through-holes 218 for allowing cuttings generated during reaming and/or material that passes through the centralizer 212 to pass through the cutter mounting plate 33 from the front side 208 to a back side 220 of the cutter mounting plate 33. A vacuum intake 222 of a cuttings removal system can be provided near the back side 220 of the cutter mounting plate 33 for drawing-in material that passes through the through-holes 218. The cuttings removal system can include a vacuum source 65 (e.g., a vacuum source above ground or at the distal end of the hole) that applies vacuum to a vacuum passage that extends from the vacuum source, through the drill string, to the vacuum intake 222. In this way, the cuttings removal system can draw cuttings and drilling fluid out of the reamed hole and can convey the cuttings and drilling fluid to a storage receptacle outside the reamed hole.

Gasketing can be provided between the vacuum intake and the back side of the cutter mounting plate to enhance suction. Fins or other structures can be provided on a front side of the cutter mounting plate for directing/lifting cuttings from the bottom of the reamed hole toward the through-holes. In one example, the reaming cutters define a cutting diameter that is at least 5, 10, or 20 percent larger than a cross-dimension (e.g., outer diameter) of the centralizer.

Referring to FIGS. 3-6, an alternative embodiment of a push reaming apparatus is described in further detail. In the depicted embodiment the drill head 100 is configured to connect to a distal end of the drill string 24 via a connection interface 102 on a second end portion 104 of the drill head 100. The drill head includes a main body 106 that supports a rotatable drive stem 108 that extends coaxially therethrough. The drive stem 108 is configured to rotate the cutter mounting plate 110. The cutter mounting plate 110 includes a front face 112 that includes a plurality of reaming cutters 114 mounted to peripheral portion 116 of the cutter mounting plate 110. The cutter mounting plate 110 includes a plurality of spaced apart through-holes 118 located around the periphery portion 116 of the cutter mounting plate 110. In the depicted embodiment the through-holes 118 are open to and coincident with the periphery edge 120 of the cutter mounting plate 110.

In the depicted embodiment the drill head 100 includes an attachment structure 122 that extends forwardly from the cutter mounting plate 110. The attachment structure 122 connects a centralizer 124 to the drill head 100. In the depicted embodiment centralizer 124 can idle (not rotate) while the cutter mounting plate 110 rotates.

In the depicted embodiment the drill head 100 includes a finished bore guide 126. The finished bore guide 126 provides additional stabilization to the drill head and also collects the cutting from the bore via vacuum intake 128 that faces and is rearward of the back side 130 of the cutter mounting plate 110. As the drill head 100 advances, cuttings are driven into the vacuum intake 128 and vacuumed through the central passage 130 of the drill head 100. In the depicted embodiment the finished bore guide 126 is generally cylindrical in shape with an outer diameter that is slightly smaller than the diameter of the reamed bore diameter. In the depicted embodiment the finished bore guide includes straight sidewalls 170 (i.e., the finished bore guide is in the shape of a constant diameter cylinder) and includes small tapers 172, 174 at both the leading edge and the trailing edge. It should be appreciated that in alternative embodiments the finished bore guide could include a tapered side wall, for example, wherein the diameter of the finished bore guide increases from the distal end to the proximal end. In the depicted embodiment the finished bore guide 126 includes a two-piece construction including a first section 176 and a second section 178 such that the finished bore guide 126 can be attached and detached from the drill head 100.

Referring to FIG. 4 the assembly of the drill head 100 is described in further detail. In the depicted embodiment the drive stem 108 is coaxially positioned within sleeve 132. The sleeve 132 is fixed to the main body 106, which is generally cylindrical. The drive stem 108 is hex fit into an end plate 134. The end plate 134 is bolted to an inner bearing housing 136. The bearing housing 136 is bolted to the cutter mounting plate 110 and rotates with the cutter mounting plate 110.

In the depicted embodiment, a first bearing assembly 138 is arranged within the bearing housing 136 to allow the bearing housing 136 to rotate relative to the sleeve 132, which is fixed to the main body 106. The first bearing assembly 138 includes a pair of thrust bearings 150, 152 positioned between a pair of radial bearings 154, 156. A second bearing assembly 140 is arranged within the bearing housing 136 and allows a centralizer shaft 142 to remain stationary or idle relative to the drive stem 108 and the cutter mounting plate 110. The second bearing assembly 140 includes a pair of thrust bearings 158, 160 that are located on the centralizer shaft 142 between a shoulder 162 and a collar 164.

In the depicted embodiment the bearing housing 136 includes a first portion that encloses the first bearing assembly 138. The first portion includes a rear portion 143 and a front portion 146. The front portion 146 includes telescoping construction with a shoulder for seating the cutter mounting plate 110. The bearing housing 136 includes a second portion 148 that encloses the second bearing assembly 140. The second portion 148 has an outer diameter that is less than a central aperture in the mounting plate 110. This configuration allows the mounting plate 110 to be connected and disconnected from the drill head 100 without disassembling the bearing housing 136.

In the depicted embodiment the centralizer 124 is bolted to a distal end 180 of the centralizer shaft 142. The centralizer shaft includes a stepped first shoulder 166 and second shoulder 168 that cooperatively seat and provides stability to the centralizer 124. The configuration enables the centralizer 124 to be connected and disconnected to the drill head without disassembling the bearing housing 136 and without removing the cutter mounting plate 110. In the depicted embodiment the distal end 180 of the centralizer shaft 142 is threaded to receive a nut 144 that secures the centralizer 124 to the centralizer shaft 142.

The drill head 100 is configured such that it can be used to enlarge a bore by thrusting/pushing it through a pilot bore. Product material such as sections of sewer pipe, water lines, conduit, etc. can be attached rearward of the finished bore guide 126 and be pulled into the bore simultaneous with the reaming process. In one embodiment the product material would be attached to the drill head 100 at a first pit and dragged by the drill head 100 to an end location. The end location could be a second pit, another pipe, a crawl space, the basement of a building, etc. This method of installing product material deployed from the first pit wherein the boring machine is especially useful wherein the far end of the bore (the exit of the bore) is not conducive to the deployment of product material. For example, when the far end of the bore is in the basement of a building, it can be difficult to get product material into the basement so that it can be pulled back through the bore during a back reaming operation. In such an application, push reaming provides significant advantages.

In the depicted embodiment the drill head 100 is constructed such that the centralizer 124, the cutter mounting plate 110, and the finished bore guide 126 are all interchangeable. In the depicted embodiment the centralizer 124, the cutter mounting plate 110, and the finished bore guide 126 can all be replaced without opening up the bearing housing 136. As discussed above, the centralizer 124 can be removed by removing a single nut 144. Once removed, the cutter mounting plate 110 can be removed by unbolting it from the bearing housing flange 182. The finished bore guide 126 can be removed by unbolting the first section 176 and a second section 178. The finished bore guide can be removed and replaced independently. In other words, it can be removed and replaced without first removing the centralizer 124 or the cutter mounting plate 110. This modular configuration provides advantages as the selection of components can be optimized based on ground conditions. For example, when drilling through softer materials, the outer size of the centralizer 124 may be very close to the diameter of the pilot hole, and the other size of the bore guide may be very close to the diameter of the bore that is reamed by the cutters on the cutter mounting plate 110. In ground conditions that are more stable or harder, it may be desirable to allow for more clearance between the pilot bore and the centralizer by using a smaller centralizer and more clearance between the reamed bore and the finished bore guide.

In the embodiment depicted above, the push reaming unit comprises the following features: a cutter mounting plate that rotates about an axis of rotation, the cutter mounting plate including a front side having a peripheral portion, the cutter mounting plate defining at least one through path that extends through the cutter mounting plate from the front side to a rear side; a plurality of reaming cutters mounted at the peripheral portion of the front side of the cutter mounting plate, the reaming cutters being spaced about the axis of rotation; a centralizer positioned in front of the cutter mounting plate, the centralizer being co-axially aligned along the axis of the rotation; an attachment structure that connects the centralizer to the cutter mounting plate; and a finished bore guide located rearward of the cutter mounting plate, the finished bore guide being removable without first removing the cutter mounting plate or centralizer. In the depicted embodiment the centralizer is attached to a centralizer shaft which is supported by a housing that rotates with the cutter mounting plate such that the shaft can rotate independent of the housing. The centralizer is cylindrical and has a maximum diameter that is smaller than a maximum diameter of the cutter mounting plate and the finished bore guide includes a maximum diameter that is larger than a maximum diameter of the centralizer. The unit also includes a finished bore guide located rearward of the cutter mounting plate, the finished bore guide includes a vacuum intake to receiving cuttings from the bore and directing the cuttings into the drill string. In the depicted embodiment the through path that extends through the cutter mounting plate from the front side to a rear side is open to a periphery edge of the cutter mounting plate. It should be appreciated that many alternative configurations are also possible.

In one embodiment a push reaming unit according to the present disclosure includes: a generally cylindrical main body portion configured to mate with a drill string; the main body including a sleeve fixedly mounted coaxially therein; a drive stem supported within the sleeve; a bearing housing fixed to the drive stem such that the bearing housing rotates with the drive stem; a first bearing assembly located within the bearing housing and configured to allow for relative rotation between the drive stem and the sleeve; a cutter mounting plate connected to the bearing housing such that the cutter mounting plate rotates with the bearing housing; a centralizer shaft extending forwardly of the cutter mounting plate from the bearing housing; a second bearing assembly located within the bearing housing and configured to allow for relative rotation between the bearing housing and the centralizer shaft; a centralizer supported on the centralizer shaft forward of the cutter mounting plate; and a finished bore guide coaxially arranged with the main body positioned rearward of the cutter mounting plate, the finished bore guide including a cutting vacuum inlet. In the embodiment depicted in FIGS. 3-5 the cutter mounting plate has a scalloped periphery edge with the scallops located between adjacent cutter mountings. The cutter mounting plate is shown bolted to a radially extending flange of the bearing housing. The centralizer shaft includes a step shoulder configuration that secures the centralizer in the radial direction. The vacuum inlet is located on the bottom portion of the finished bore guide and is configured to funnel cuttings into the cuttings conduit of the main body which position below a sight path that extends through the main body of the drill head. It should be appreciated that many alternative configurations are also possible which may include more or fewer features as well as different features. For example, it should be appreciated that fluid such as water can be delivered to the bore via hoses to aid in flushing of the cutting out of the bore.

The present disclosure provides a method of push reaming that in one embodiment includes the following steps: selecting a centralizer or a drill head based on the diameter of a pilot bore; selecting a finished bore guide based on the diameter of the final reamed bore diameter and also in part on the ground condition in which the reaming will be done; connecting the centralizer to a drill head forward of a cutter mounting plate; connecting the finished bore guide rearward of the cutter mounting plate; thrusting the drill head into the pilot bore while rotating the cutter mounting plate; and removing cuttings from the bore via a vacuum inlet located rearward of the cutter mounting plate and forward of a rear portion of the finished bore guide. In the embodiment disclosed in FIGS. 3-5, the centralizer is not driven to rotate even when the cutter mounting plate rotates. As discussed above the finished bore guide in the embodiment depicted in FIGS. 3-5 can be detached from the drill head without detaching the centralizer or the cutter mounting plate from the drill head. As discussed above, the cutter mounting plate in the embodiment depicted in FIGS. 3-5 is bolted to an annular flange of a bearing housing. It should be appreciated that alternative embodiments may include fewer steps, different steps, and/or a different combination of steps

Various modifications and alterations of this disclosure will become apparent to those skilled in the art without departing from the scope and spirit of this disclosure, and it should be understood that the scope of this disclosure is not to be unduly limited to the illustrative examples set forth herein. 

What is claimed is:
 1. A push reaming unit comprising: a cutter mounting plate that rotates about an axis of rotation, the cutter mounting plate including a front side having a peripheral portion, the cutter mounting plate at least partially defining at least one through path that extends through the cutter mounting plate from the front side to a rear side; a plurality of reaming cutters mounted at the peripheral portion of the front side of the cutter mounting plate, the reaming cutters being spaced about the axis of rotation; a centralizer positioned in front of the cutter mounting plate, the centralizer being co-axially aligned along the axis of the rotation.
 2. The push reaming unit of claim 1, wherein the cutter mounting plate and centralizer are arranged and configured such that they can rotate relative to each other.
 3. The push reaming unit of claim 1, wherein the centralizer is attached to a centralizer shaft which is supported by a bearing housing that rotates with the cutter mounting plate such that the centralizer shaft can rotate independent of the bearing housing.
 4. The push reaming unit of claim 1, wherein the centralizer is generally cylindrical and has a maximum diameter that is smaller than a maximum diameter of the cutter mounting plate.
 5. The push reaming unit of claim 1, further comprising a finished bore guide located rearward of the cutter mounting plate, the finished bore guide including a maximum diameter that is larger than a maximum diameter of the centralizer.
 6. The push reaming unit of claim 1, further comprising a vacuum intake positioned rearward of the cutter mounting plate and configured to not rotate with the cutter mounting plate.
 7. The push reaming unit of claim 1, further comprising a finished bore guide located rearward of the cutter mounting plate, the finished bore guide includes a generally cylindrical rear portion as well as a vacuum intake for receiving cuttings from the bore and directing the cuttings into the drill string.
 8. The push reaming unit of claim 1, wherein the through path that extends through the cutter mounting plate from the front side to the rear side is open to a periphery edge of the cutter mounting plate.
 9. The push reaming unit of claim 1, further comprising a finished bore guide located rearward of the cutter mounting plate, the finished bore guide being removable from the push reaming unit without first needed to remove the cutter mounting plate or centralizer from the push reaming unit.
 10. A push reaming unit comprising: a generally cylindrical main body portion configured to mate with a drill string; the main body including a sleeve fixedly mounted coaxially therein; a drive stem coaxially arranged within the sleeve; a bearing housing fixed to the drive stem such that the bearing housing rotates with the drive stem; a first bearing assembly located within the bearing housing and configured to allow for relative rotation between the drive stem and the sleeve; a cutter mounting plate connected to the bearing housing such that the cutter mounting plate rotates with the bearing housing and the drive stem; a centralizer shaft extending forwardly of the cutter mounting plate outwardly from the bearing housing; a second bearing assembly located within the bearing housing, the second bearing assembling being configured to allow for relative rotation between the bearing housing and the centralizer shaft; a centralizer mounted to the centralizer shaft forward of the cutter mounting plate, the centralizer being decoupled from rotation of the dive stem; and a finished bore guide coaxially arranged with the main body portion position rearward of the cutter mounting plate, the finished bore guide including a cross sectional diameter that is larger than the cross sectional diameter or the main body portion and as well as the centralizer; a cutting vacuum inlet provided on the finished bore guide, the vacuum inlet being at least partially facing the cutter mounting plate.
 11. The push reaming unit of claim 10, wherein the cutter mounting plate has a scalloped periphery edge with at least one scallop is located between adjacent cutter mountings on the cutter mounting plate.
 12. The push reaming unit of claim 10, wherein the cutter mounting plate is bolted to a radially extending flange of the bearing housing and there the cutter mounting plate is arranged and configured such that it can be removed from the push reaming unit without disassembling the bearing housing.
 13. The push reaming unit of claim 10, wherein the centralizer shaft includes step shoulder configuration that secure the centralizer in the radial direction.
 14. The push reaming unit of claim 10, wherein the vacuum inlet is located on the bottom portion of the finished bore guide and is configured to funnel cuttings into the cuttings conduit of the main body which is positioned below a sight path.
 15. A method of push reaming comprising: selecting a centralizer or a drill head based on the diameter of a pilot bore; selecting a finished bore guide based on the diameter of the final reamed bore diameter; connecting the centralizer to a drill head forward of a cutter mounting plate; connecting the finished bore guide rearward of the cutter mounting plate; and thrusting the drill head into the pilot bore while rotating the cutter mounting plate.
 16. The method of claim 15, wherein the centralizer is not driven to rotate even when the cutter mounting plate is driven to rotate.
 17. The method of claim 15, removing cutting from the bore via a vacuum inlet, the vacuum inlet being located rearward of the cutter mounting plate and forward of a rear portion of the finished bore guide.
 18. The method of claim 15, connecting the finished bore guide to the drill head without first detaching the centralizer or the cutter mounting plate from the drill head.
 19. The method of claim 15, wherein the selection of the finished bore guide is also based in part on the ground condition in which the reaming will be done.
 20. The method of claim 15, wherein the cutter mounting plate is bolted to an annular flange of a bearing housing. 